The present invention relates to a method of making an integrated circuit device package, and in particular to a die attachment method using an adhesive film, and a tool system for performing the die attachment method.
Integrated circuit packages typically include an integrated circuit die attached to a substrate. Bond wires or equivalent conductors are connected between the integrated circuit die and metallizations on the substrate. The metallizations are connected to other metal structures of the substrate, such as bonding pads or solder balls, for connecting the package to a printed circuit board.
Typically, a plurality of packages are built in parallel on substrate strip. The strip may be formed, for example, of a thin insulative film such as a polyimide film or an epoxy laminate film. Alternatively, the substrate strip may be an array of interconnected metal leadframes.
Conventional substrate strips include a plurality of die mounting sites. A die is attached to each mounting site of the substrate strip. Subsequently, the dies are each wire bonded to the metallizations of their respective mounting site, and the mounting sites are encapsulated. Finally, the substrate is cut with a saw or punch to form individual packages.
An increasingly common way to attach a die to a substrate strip is to use an adhesive film, such as a B-staged epoxy film. Another adhesive film available from the W. L. Gore Co. of Arizona is formed of a Teflon-like carrier material coated with adhesives. Such adhesive films characteristically require the application of pressure and heat for the adhesive to cure.
A conventional method of attaching a die 10 to a substrate strip 11 is shown in FIG. 1A. An initial step involves placing an adhesive film 12 on each die mounting site of substrate strip 11. Next, a conventional die attachment tool 13 is used to place a die 10 on the adhesive film 12 of each site of substrate strip 11. Pick-up head 14 of tool 13 picks up a die 10 from a cut wafer, indexes die 10, and places the die 10 on adhesive film 12. Head 14 and lower plate 15 of tool 13 press together and apply pressure and temperature to die 10, adhesive film 12, and substrate strip 11 for a selected period of time to cure adhesive film 12. Subsequently, head 14 detaches from the surface of die 10, picks up another die 10, and repeats the process. In particular, an erroneous reference to FIG. 1 is changed to FIG. 1A. No new matter is added.
Conventionally, the above-described placement and curing steps are done one die at a time until each package site of substrate strip 11 has a die 10 attached to it, as shown in FIG. 1B. Hence, the time to place and attach each die 10 to the substrate strip 11 is the sum of the placement time and the curing time. Typically, placing a die 10 on an adhesive film 12 of substrate strip 11 takes one second, and curing adhesive film 12 takes between 2 and 4 seconds, depending on the materials used and the area of the die. Accordingly, the attachment time for each die 10 is between 2 and 5 seconds. This time is then multiplied by the number of die 10 to determine the total processing time for each substrate strip 11. For a substrate strip 11 having 100 package sites, for example, the conventional die placement and attachment process takes at least 200 to 500 seconds to complete.
Artisans will appreciate that the cost of packaging an integrated circuit die depends, in part, on the efficiency of the assembly process. Accordingly, improvements in efficiency are highly desirable.
The present invention can provide orders of magnitude improvement in the efficiency of the die attachment process when using an adhesive film to attach a die to a substrate strip.
A method within the present invention includes placing an integrated circuit die onto an adhesive film at each package site of a substrate strip. The placement operation is continuous, that is, a die is placed on each of a plurality of die mounting sites until the substrate strip is fully populated. Subsequently, the adhesive films of a plurality of sites are simultaneously cured by applying heat and pressure to the plurality of sites. The method increases the throughput of the die attachment process because the curing step is a batch process, whereas in the prior art, the curing step was performed one die at a time immediately after placement of the particular die.
An embodiment of a tool system within the present invention for accomplishing the above process has two stations: (1) a die attach station; and (2) a batch curing station.
These and other objects, features and advantages of the present invention will be more readily apparent from the figures and the detailed description set forth below.